Intravascular ultrasound is a technology developed over the last 5 years that uses high frequency soundwaves to generate cross sectional images of vascular structures. These images contain microanatomic information of the geometry and tissue composition of the vascular wall. This method provides for the first time in vivo a means to interrogate vascular structures and assess the development of intimal hyperplasia, atherosclerosis or regression of disease. This technology has already had significant impact on our clinical understanding of the pathophysiology of atherosclerosis as well as on the effects of various interventional devices to treat coronary artery disease. The purpose of this proposal is to continue our investigation into the clinical uses of intravascular ultrasound imaging and to better understand the correlation between the ultrasound images and histologic morphology. The main hypothesis to be tested is that intravascular ultrasound imaging can be applied to guide interventions in coronary artery disease which will result in less complications and diminished restenosis rates. The interventions to be investigated re coronary atherectomy, stent implantation, and assessment of atherosclerosis progression or regression.